Study of an underexpanded plasma jet

Supersonic jets (Mach number M = 1.4-2.0) of dense plasma were produced by a plasmatron in a pulsed regime. The shock structure was investigated by fast mirror cameras, by the schlieren technique and by probe and spectroscopic methods. It was found that during jet expansion the bow schock ahead the gas-plasma interface and the shock behind it are superimposed with the quasi-stationary shock structure which includes the Mach disk. Whereas the plasma in the discharge chamber is in LTE (ne ∼ 5 x 1023 m-3, T ∼ 14000 K), the electron density of the expanding jet plasma falls to a plateau value of ne ∼ 5 x 1019 m-3 below the LTE limit. At this phase, the jet plasma formed a ball-like turbulent plasmoid which moves at a subsonic velocity through the air up to some milliseconds. (author)